Answer: The number of substrate molecules converted per enzyme molecule per second.
- A The fixed number of substrate molecules an enzyme requires to become active
- B The number of substrate molecules converted per enzyme molecule per second
- C The rate at which new enzyme molecules are transcribed and translated
- D The rate at which a competitive inhibitor binds the enzyme's active site
Correct answer: B. The number of substrate molecules converted per enzyme molecule per second
Explanation: kcat (catalytic constant or turnover number) is the maximum number of substrate molecules converted to product per enzyme molecule per second. Catalase has a very high kcat (~4 million/s).
As substrate concentration rises, reaction rate increases steeply at first, then plateaus at Vmax once every enzyme molecule is working at full capacity; Km is the substrate concentration giving half-maximal rate, and a LOWER Km means the enzyme reaches that rate with less substrate (higher affinity).
Concept context
Carbohydrates, proteins, lipids, nucleic acids, and enzyme kinetics. Essential foundation for understanding metabolism.